Clarkson 5" A3 Rebuild

[coniston]

I've had a bit of a non progressive day today, I am trying to weld my own superheaters from stainless tube. To start with I have lots of 1/4" tube so started having a go with that. The ones for the A3 are going to be 5/16" but I don't have so much spare of that size although I did a couple of short pieces as you'll see below. If successful (eventually) I will need to make new ones for a 'Pansy' I have under the bench for complete restoration, so long term this ability will be useful as well as self satisfaction.


I started by making a rough and ready cutting aid to get the ends sawn at the same angle, I chose 20 degrees each giving included angle of 40 degrees for no other reason than It looked about right.




Then came all the fun and games of trying to weld the little buggers together. I made a simple clamp from a couple of steel bars to hold them together for initial welding.



The points and sides were no problem at all, no filler rod just using the parent material making a nice smooth weld. As expected the difficult bit is getting through the 'V', that calls for extending the TIG tungsten as far out as practical, in my case about 3/4", upping the argon flow and trying not to touch the tubes with the tungsten. I tried adding filler rod to help the joint but ended up with big blobs that wouldn't flow into the weld puddle or touching the tungsten or welding the rod and tungsten to the tune. All very frustrating! Any way I eventually did get a couple that didn't leak when blown through under water but heavens knows if they will stand up to hydraulic test. Photos of trial pieces with the best one in closeup. 





I tried bending them parallel with a piece of 1/2" steel bar between the tubes so as to relieve pressure on the weld and prevent the inside of the 'V' from crushing, at least that bit worked and it slips easily into the super heater flue which is 1 1/8" I/D.

I'll continue tomorrow, I have a couple of other ideas to try maybe using block type return bends from stainless or making a sheet cover to go inside the 'V' so I don't have to weld right down into the corner. 

What it has shown is what good value the purchased items are considering all the hassle I've been through today and the time taken, so may just end up getting them made or at least taking the prepared tubes to a friendly local company who might just TIG round the points for me.

Let's see what tomorrow brings.

Chris D

[andyhigham]

Concentrics are much easier

[coniston]

Apr 10, 2020 20:43:21 GMT andyhigham said:

Concentrics are much easier

Yes but from what I've read/heard they don't work that well, and from looking at the principal of them I agree. I still favour radiant super heaters or don't bother with them at all. 

Chris D

[andyhigham]

The only way to put that argument to bed would be to fit one of each to a loco and install a thermocouple on the cylinder end of each superheater. Then log the temperatures during a running session.

My personal view is that the return leg of a hairpin radiant superheater will be losing heat to the flue gasses. A concentric with the return up the middle will only lose heat to the incoming steam thus keeping the heat in the system

[Roger]

Welding superheater points is a reall challenge, although you've made it much easier by choosing the style you have.
Just a few observations based on my own frustrations of doing something similar.

1) You need to have secondary Argon flowing through the tubes, else you risk getting 'sugaring' on the inside.
2) Although you can weld the tip and about 3/4 of the way round without filler rod, I'd suggest that you stop at that point and then switch to a different technique with filler wire. The problem is that the amount of heat you need to complete the weld is much more when you go round to the bottom of the joint.

It's very easy to come unstuck and blow a hole through as you go round to the middle. Getting it to seal to the middle ought to be easier doing it like you are. The design I've used makes it really hard to do that, combined with the fact that I'm using 0.7mm thick tube.

Is your tube 316L? That's what I was told I'd need.

My opinion is that the hairpin type is more effective, for the reasons that there is a greater surface area of tube in contact with the flue gasses, and the temperature of the two tubes can be significantly different. I'd suggest that means you ought to have greater heat transfer and also a higher outlet temperature.

Here's a link to the way I did it.

[uuu]

Apr 10, 2020 21:21:33 GMT andyhigham said:

The only way to put that argument to bed would be to fit one of each to a loco and install a thermocouple on the cylinder end of each superheater. Then log the temperatures during a running session.

My personal view is that the return leg of a hairpin radiant superheater will be losing heat to the flue gasses. A concentric with the return up the middle will only lose heat to the incoming steam thus keeping the heat in the system

I believe this experiment has been done, and the hairpin style was superior. There are all sorts of quasi-thermodynamic arguments in favour/against each type, but the experiment was properly arranged (was it Jim Ewins?), so appears to trump the discussion.

Nevertheless, I shall be fitting the concentric type to my own loco. Everything is a compromise.

Wilf

[coniston]

Apr 10, 2020 21:48:38 GMT Roger said:

Welding superheater points is a reall challenge, although you've made it much easier by choosing the style you have.
Just a few observations based on my own frustrations of doing something similar.

1) You need to have secondary Argon flowing through the tubes, else you risk getting 'sugaring' on the inside.
2) Although you can weld the tip and about 3/4 of the way round without filler rod, I'd suggest that you stop at that point and then switch to a different technique with filler wire. The problem is that the amount of heat you need to complete the weld is much more when you go round to the bottom of the joint.

It's very easy to come unstuck and blow a hole through as you go round to the middle. Getting it to seal to the middle ought to be easier doing it like you are. The design I've used makes it really hard to do that, combined with the fact that I'm using 0.7mm thick tube.

Is your tube 316L? That's what I was told I'd need.

My opinion is that the hairpin type is more effective, for the reasons that there is a greater surface area of tube in contact with the flue gasses, and the temperature of the two tubes can be significantly different. I'd suggest that means you ought to have greater heat transfer and also a higher outlet temperature.

Here's a link to the way I did it.

Thanks Roger for sharing that, I had thought you might have come up with some good way of doing it, I missed that in your thread, probably before I joined and started following your work. I'll have a thorough look through all your photos and take what I can from them.

Chris D

[Roger]

Apr 11, 2020 19:44:07 GMT coniston said:

Apr 10, 2020 21:48:38 GMT Roger said:

Welding superheater points is a reall challenge, although you've made it much easier by choosing the style you have.
Just a few observations based on my own frustrations of doing something similar.

1) You need to have secondary Argon flowing through the tubes, else you risk getting 'sugaring' on the inside.
2) Although you can weld the tip and about 3/4 of the way round without filler rod, I'd suggest that you stop at that point and then switch to a different technique with filler wire. The problem is that the amount of heat you need to complete the weld is much more when you go round to the bottom of the joint.

It's very easy to come unstuck and blow a hole through as you go round to the middle. Getting it to seal to the middle ought to be easier doing it like you are. The design I've used makes it really hard to do that, combined with the fact that I'm using 0.7mm thick tube.

Is your tube 316L? That's what I was told I'd need.

My opinion is that the hairpin type is more effective, for the reasons that there is a greater surface area of tube in contact with the flue gasses, and the temperature of the two tubes can be significantly different. I'd suggest that means you ought to have greater heat transfer and also a higher outlet temperature.

Here's a link to the way I did it.

Thanks Roger for sharing that, I had thought you might have come up with some good way of doing it, I missed that in your thread, probably before I joined and started following your work. I'll have a thorough look through all your photos and take what I can from them.

Chris D

You're most welcome Chris. It's tricky to get right, and I'm still improving the method. My main problem is seeing really clearly what's going on. I've now got the most powerful 'cheater lens' and fitted that to my welding mask, and that certainly helps. Ideally, I'd like to use some sort of camera and really blow up a clear image on a screen. That would make life a lot easier.
If you look at my thread on page 305 onwards, you'll see how I did mine. It's certainly not the easiest way, and I need to do more work on the method. One thing I've done is to make a forming punch that I drive into the end of the sloping cut. That puts a nice flat on the inside of the tube which makes it easier to achieve the initial root weld. The big problem is still connecting to that when welding from the tip round to the join. If I can crack that reliably, then it would be a good method. At the moment, I reckon I only get one good one out of every two or three that I weld. Not a good ratio. One day when I've finished all this, I might return to the subject with a view to selling them commercially.

[steamer5]

Hi Chris,
You could always go down this route & avoid welding altogether

www.cheltsme.org.uk/index-superheaters.html?

On my replacement elements a friend welded the blocks I had made to the tubes, he nailed weld between the tubes first go & there wasn’t much of a gap

Cheers Kerrin

[Roger]

Apr 11, 2020 22:54:10 GMT steamer5 said:

Hi Chris,
You could always go down this route & avoid welding altogether

www.cheltsme.org.uk/index-superheaters.html?

On my replacement elements a friend welded the blocks I had made to the tubes, he nailed weld between the tubes first go & there wasn’t much of a gap

Cheers Kerrin

Hi Kerrin,
I'm amazed those seal with just Boss White. I'd be surprised if they stay sealed for long, but I may be wrong. It just sounds like a bit of a bodge to me.

[steamer5]

Hi Roger,
Yep you & me both! But the gent says he’s been using them ok. I seem to recall a discussion on this idea somewhere, can’t recall were, as you say there was a amazed that this would work.
Maybe we have somebody here from the club who maybe able to update us as to wether it’s working or not as the case maybe. Either way it solved a bunch of issues with making superheaters!

So for those of us from Downunder ......what’s Boss White? I’m guessing a pipe thread sealant, & also that it shouldn’t work in this type of service!

Stay safe.


Cheers Kerrin

[Roger]

Apr 12, 2020 8:36:44 GMT steamer5 said:

Hi Roger,
Yep you & me both! But the gent says he’s been using them ok. I seem to recall a discussion on this idea somewhere, can’t recall were, as you say there was a amazed that this would work.
Maybe we have somebody here from the club who maybe able to update us as to wether it’s working or not as the case maybe. Either way it solved a bunch of issues with making superheaters!

So for those of us from Downunder ......what’s Boss White? I’m guessing a pipe thread sealant, & also that it shouldn’t work in this type of service!

Stay safe.


Cheers Kerrin

Hi Kerrin,
It certainly does save a lot of headaches. Yes, Boss White is a product that does back to the dawn of civilisation. It's a sticky 'gunk' that gets absolutely everywhere and is used on pipe fittings. It goes hard over time, so perhaps it has refractory properties when incinerated. It mostly was used where we use Silicone sealants today.

[uuu]

Yes, it's a pipe sealant. I haven't seen any for years, but remember it being used with hemp fibres on threaded gas pipe joints. I see it's still listed for sale - £3.48 for a 400g tub. Claims it's suitable for high temp.


BOSS product brochure

Wilf

[andyhigham]

I've just had a lightbulb moment! It would look like the superheaters in the article but welded and all the welds accessible
A disc of stainless steel with 2 holes the superheater tubes would push into. The tubes are then welded to the disc around the end circumference.
A cap then machined like a closed end thimble and welded around the circumference of the disc

With a milling machine the disc and cap could be oval

[Roger]

Apr 12, 2020 9:07:10 GMT andyhigham said:

I've just had a lightbulb moment! It would look like the superheaters in the article but welded and all the welds accessible
A disc of stainless steel with 2 holes the superheater tubes would push into. The tubes are then welded to the disc around the end circumference.
A cap then machined like a closed end thimble and welded around the circumference of the disc

With a milling machine the disc and cap could be oval

That would certainly solve the key problem, which is welding where the two tubes are closest together. The plate could be thick enough to prevent it burning straight through. I'm sure this idea would work and be easier to weld.
Welding of the outer thimble would be made easier if the flat plate was say 2-3mm thick and the thimble didn't cover all of it. Then you could weld on the outside rather than trying to weld onto the back face.
There's no reason why the two tubes couldn't be butted up against each other in the plate. You can weld onto the face of the tubes. The tubes could protrude slightly, say 0.2-0.3mm to provide a little 'filler' material as it melts back to the plate.

I think this idea has real promise. It's not very elegant, but then again, it's not seen.

The only thing that would be an issue is in getting the diameter small enough. It might be best to make the tube disc over size, then make a fixture so it could be turned down after welding so that the diameter is brought back to the edge of the tube. Then the thimble thickness is all there is over the outside, and that doesn't need to be more than say 0.7mm which is my tube thickness anyway.

[uuu]

Part of the "spear point" shape of the end would be to aid the flow around it in the flue, I suppose. But if you're going radiant then any old shape would do, as long as goes down the tube for fitting.

Wilf

[Roger]

Apr 12, 2020 9:51:17 GMT uuu said:

Part of the "spear point" shape of the end would be to aid the flow around it in the flue, I suppose. But if you're going radiant then any old shape would do, as long as goes down the tube for fitting.

Wilf

True, and to be honest, there probably isn't much point in fitting Superheaters that aren't of the Radiant type.

[andyhigham]

A quick sketch and it looks feasible
20200412_120708 by Sigma Projects, on Flickr

[coniston]

Guys, I think you've just come up with a very workable solution, the ends can be oval. And if shaped like Andy is suggesting in his sketch would promote good gas flow. I can see an experiment coming on tomorrow. Unfortunately I'm pretty much out of Argon now so have to wait until Tuesday to see if my supplier can deliver some, generally they are ok with delivery so I'm keeping my fingers crossed. But I can get on with making the bits to try out. Luckily the Don Young A3 boiler carries 1 1/4" O/D super heater flues, so 1 1/8" I/D, plenty of room for the end pieces and two 5/16" super heater tubes.

Many thanks for your thoughts.

Chris D

[andyhigham]

With flues that big you could easily fit 4 tubes into each return. That would slow the steam flow down by half so the steam would spend twice as long in the firebox.